It has been reported that compound A has a selective affinity for the muscarinic acetylcholine receptor (M1 receptor) and hydrochloride, fumarate, maleate and di-p-toluoyl-D-tartrate of compound A can be utilized in the treatment of diseases associated with a deficiency of acethylcholine-related functions, such as Alzheimer's disease (JP-A-2-36183; the term "JP-A" as used herein means an "unexamined published Japanese patent application").
JP-A-2-36183 enumerates various inorganic and organic acid addition salts which can be formed by heterocyclic spiro compounds such as compound A, including addition salts with tartaric acid. However, the literature contains no specific disclosure of the tartrate of compound A or its monohydrate.
On the other hand, compound A as the free base is oily and can be crystallized after conversion to certain acid addition salts. The research undertaken by the inventors of the present invention revealed that compound A does not form a crystallizable salt with D-tartaric acid, D- or L-malic acid, succinic acid, hydrobromic acid, sulfuric acid, phosphoric acid or the like. The hydrochloride gave a powdery compound which, however, underwent deliquescence within 24 hours when allowed to stand in the air, due to high hygroscopicity.
Meanwhile, stability of compound A is low even in the form of a solid salt and this instability has been a major drawback in the practical application of this compound as a medicinal material.